High power infrared lasers are capable of projecting a beam of invisible radiation over great distances, producing very large amounts of heat in any material substance which intersects the beam. A method for determining the position and irradiance distribution of the laser beam on a remotely-located target is required to assess the performance of the laser and for bore-sighting the beam transmitter. Because of the very high energy associated with the laser beam, active infrared detectors and sensors cannot be used.
Conventional passive, high power infrared laser irradiance display materials (such as zirconium dioxide or hafnium dioxide) perform the functions of laser spot location and display of their radiance distribution by simply absorbing the laser radiation, converting it to heat, and reradiating visible radiation, thus providing a pattern of visible radiation in known relationship to the infrared laser radiation. These materials must be refractory, to withstand the high temperatures, have a high absortivity for the laser radiation and have a high emissivity for visible radiation. They should also possess good mechanical strength, resistance to oxidation and be easy to fabricate into desired shapes. As the incident laser irradiance is increased, however, any material which has a high absorptivity for the laser radiation will eventually absorb enough energy to melt, sublime, vaporize, or otherwise degrade. For the conventional passive irradiance display materials, the maximum continuous-wave CO.sub.2 laser irradiance is of the order of a few kilowatts per cm.sup.2. This irradiance is much below that which can be produced by state-of-the-art high-power laser devices.
An object of this invention is to provide a method for laser spot location and irradiance display at irradiances much higher than current state-of-the-art techniques, using the principles of partial reflection of the laser radiation and heat-sinking of the absorbed energy.
A further object of this invention is to provide a material which can withstand very high laser irradiances without degradation, and perform the functions of passive infrared laser spot location and irradiance display.